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terior spiracles (Carpenter and Hewitt) 
4 
Ventrally segments 2 to 9 are provided fairly con- 
‘stantly with a heavy band of spines along the posterior 
‘border, but it is not uncommon to find specimens in which 
‘segment 10 is also armed and others with segment 9 
naked. The spines on the anterior borders of the seg- 
‘ments, ventrally, vary even more, and usually end on 
‘the eighth or ninth segment. Laterally the armature is 
‘very irregular and rarely extends behind the sixth seg- 
‘ment on the ventrolateral or the fourth segment on the 
‘mediolateral and dorsolateral areas. Dorsally the arma- 
‘ture is almost entirely wanting. The greater part of the 
/ anal segment posteriorly is thickly covered with small 
‘spines surrounding the posterior spiracles, but the tri- 
‘angular spines are no longer present. The two posterior 
)Spiracles may be round or very irregular in outline. 
‘They consist of a group of circular rings or disks. The 
‘color of the stigmal plate is orange or yellowish brown, 
‘and the disks are separate or loosely connected in groups 
‘but always very distinct in individual outline. The num- 
‘ber of disks varies from 12 to over 30, but usually with 
Specimens collected in Texas it is from about 18 to 25 
(fig. 14). 
|. The fourth-stage larva of H. bovis is similar to that of 
| H. lineatum, but when grown it is slightly larger. The only 
‘Specific distinguishing characters that can be relied upon 
‘are the posterior stigmal plates. In AH. bovis the stigmal 
)plates are composed of disks or rings that are dark brown 
or black in color, and usually the whole group is closely 
fused together. The number of disks in H. bovis is 
‘usually considerably higher than in H. lineatwm, running 
from 29 to above 40, with the normal number about 32 
to 37 (fig. 15). 
v3 
THE CATTLE GRUBS OR OX WARBLES 
29 
Fic. 9.—Hypoderma bovis: First-stage larva. I, Lateral view; II, ventral view; 
’ III, cephalopharyngeal skeleton with spine and mouth hooks; IV, caudal segment. 
Ph, Skeleton of pharynx; H, mouth hooks; M, spine; 77, air tubes; P. sp., pos- 
Fic. 10.—Hypoderma 
lineatum: Ventral 
view of first-stage 
larva. A, Mouth 
hooks; B, anterior 
spiracles ; C, cepha- 
lopharyngeal skele- 
ton; Fs, flattened 
spines on border of 
posterior spiracles ; 
sp., posterior 
spiracles. > <eaPal 
(Laake) 
